1. Technical Field
The present technology relates to a pneumatic tire in which main grooves extending in a tire circumferential direction are provided in a tread portion, and particularly relates to a pneumatic tire whereby traveling performance on wet road surfaces (hereinafter referred to as “wet performance”) and quietness can be improved in a well-balanced manner.
2. Related Art
Conventionally, with pneumatic tires, a plurality of main grooves extending in a tire circumferential direction is formed in a tread portion. These main grooves contribute greatly to water drainage properties. Facilitating the flow of water in the main grooves by periodically varying a groove width of the main grooves along the tire circumferential direction in order to improve the water drainage properties derived from such main grooves has been proposed (e.g. see Japanese Unexamined Patent Application Publication No. 2010-179892A). However, with the current technology, a definite improvement in wet performance cannot be achieved by simply varying the groove width of the main grooves.
Additionally, because circumferential grooves such as main grooves and the like that are formed in the tread portion are a source of air column resonance, efforts have been made to reduce noise originating from the circumferential grooves and, thereby, improve quietness. A technique has been proposed for this purpose in which vibration frequencies generated when the tread portion contacts the ground are varied along a tire circumference by branching a portion of the circumferential grooves in the tire circumferential direction (e.g. see Japanese Unexamined Patent Application Publication No. 2004-351954A). However, in this case, there is a problem in that wet performance may be insufficient because water easily accumulates in portions of the branched circumferential grooves where the grooves recombine.